System and method for minimizing write-amplification in log-structured writes

ABSTRACT

A method, computer program product, and computer system for submitting, by a computing device, a write for a write-request equal to a size of valid data in a segment. The write-request may be decomposed into RAID elements and corresponding parity stripe elements. Parity for RAID stripes may be calculated using only valid RAID elements of the RAID elements. A write for all the valid RAID elements and the corresponding parity stripe elements may be issued. An unmap command may be issued to at least a portion of the segment that is invalid.

BACKGROUND

In some log-structured storage systems, ingesting data (either newwrites or over-writes) is generally always written to an empty segment.This segment is generally parity-protected (e.g., RAID-5, RAID-6) andlarge in size (e.g., 2 MB) to minimize the number of segments that needto be tracked in the storage system. There may be several use cases whenflushing dirty data into these segments, or when ingesting new writesdirectly into these segments, that there is not enough data tocompletely fill the segment. In such a scenario, rest of the segment ispadded with zeros and parity is calculated on the full segment.

BRIEF SUMMARY OF DISCLOSURE

In one example implementation, a method, performed by one or morecomputing devices, may include but is not limited to submitting, by acomputing device, a write for a write-request equal to a size of validdata in a segment. The write-request may be decomposed into RAIDelements and corresponding parity stripe elements. Parity for RAIDstripes may be calculated using only valid RAID elements of the RAIDelements. A write for all the valid RAID elements and the correspondingparity stripe elements may be issued. An unmap command may be issued toat least a portion of the segment that is invalid.

One or more of the following example features may be included. Issuingthe unmap command to at least a portion of the segment that is invalidmay result in returning zeros on subsequent reads of the RAID elementsand corresponding parity stripe elements that are invalid in thesegment. The zeros may be returned on the subsequent reads of the RAIDelements and corresponding parity stripe elements that are invalid inthe segment without writing the zeros. The RAID elements may includesub-RAID elements. At least the portion of the segment may include RAIDelements that are invalid in the segment. At least the portion of thesegment may further include corresponding parity stripe elements thatare invalid in the segment. The segment may be parity protected usingone of RAID-5 and RAID-6.

In another example implementation, a computing system may include one ormore processors and one or more memories configured to performoperations that may include but are not limited to submitting a writefor a write-request equal to a size of valid data in a segment. Thewrite-request may be decomposed into RAID elements and correspondingparity stripe elements. Parity for RAID stripes may be calculated usingonly valid RAID elements of the RAID elements. A write for all the validRAID elements and the corresponding parity stripe elements may beissued. An unmap command may be issued to at least a portion of thesegment that is invalid.

One or more of the following example features may be included. Issuingthe unmap command to at least a portion of the segment that is invalidmay result in returning zeros on subsequent reads of the RAID elementsand corresponding parity stripe elements that are invalid in thesegment. The zeros may be returned on the subsequent reads of the RAIDelements and corresponding parity stripe elements that are invalid inthe segment without writing the zeros. The RAID elements may includesub-RAID elements. At least the portion of the segment may include RAIDelements that are invalid in the segment. At least the portion of thesegment may further include corresponding parity stripe elements thatare invalid in the segment. The segment may be parity protected usingone of RAID-5 and RAID-6.

In another example implementation, a computer program product may resideon a computer readable storage medium having a plurality of instructionsstored thereon which, when executed across one or more processors, maycause at least a portion of the one or more processors to performoperations that may include but are not limited to submitting a writefor a write-request equal to a size of valid data in a segment. Thewrite-request may be decomposed into RAID elements and correspondingparity stripe elements. Parity for RAID stripes may be calculated usingonly valid RAID elements of the RAID elements. A write for all the validRAID elements and the corresponding parity stripe elements may beissued. An unmap command may be issued to at least a portion of thesegment that is invalid.

One or more of the following example features may be included. Issuingthe unmap command to at least a portion of the segment that is invalidmay result in returning zeros on subsequent reads of the RAID elementsand corresponding parity stripe elements that are invalid in thesegment. The zeros may be returned on the subsequent reads of the RAIDelements and corresponding parity stripe elements that are invalid inthe segment without writing the zeros. The RAID elements may includesub-RAID elements. At least the portion of the segment may include RAIDelements that are invalid in the segment. At least the portion of thesegment may further include corresponding parity stripe elements thatare invalid in the segment. The segment may be parity protected usingone of RAID-5 and RAID-6.

The details of one or more example implementations are set forth in theaccompanying drawings and the description below. Other possible examplefeatures and/or possible example advantages will become apparent fromthe description, the drawings, and the claims. Some implementations maynot have those possible example features and/or possible exampleadvantages, and such possible example features and/or possible exampleadvantages may not necessarily be required of some implementations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example diagrammatic view of a write process coupled to anexample distributed computing network according to one or more exampleimplementations of the disclosure;

FIG. 2 is an example diagrammatic view of a storage system of FIG. 1according to one or more example implementations of the disclosure;

FIG. 3 is an example diagrammatic view of a storage target of FIG. 1according to one or more example implementations of the disclosure;

FIG. 4 is an example flowchart of a write process according to one ormore example implementations of the disclosure; and

FIG. 5 is an example diagrammatic view of a 4+1 2 MB segment with a 64kelement size according to one or more example implementations of thedisclosure.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

System Overview:

In some implementations, the present disclosure may be embodied as amethod, system, or computer program product. Accordingly, in someimplementations, the present disclosure may take the form of an entirelyhardware implementation, an entirely software implementation (includingfirmware, resident software, micro-code, etc.) or an implementationcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore, insome implementations, the present disclosure may take the form of acomputer program product on a computer-usable storage medium havingcomputer-usable program code embodied in the medium.

In some implementations, any suitable computer usable or computerreadable medium (or media) may be utilized. The computer readable mediummay be a computer readable signal medium or a computer readable storagemedium. The computer-usable, or computer-readable, storage medium(including a storage device associated with a computing device or clientelectronic device) may be, for example, but is not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, device, or any suitable combination ofthe foregoing. More specific examples (a non-exhaustive list) of thecomputer-readable medium may include the following: an electricalconnection having one or more wires, a portable computer diskette, ahard disk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), anoptical fiber, a portable compact disc read-only memory (CD-ROM), anoptical storage device, a digital versatile disk (DVD), a static randomaccess memory (SRAM), a memory stick, a floppy disk, a mechanicallyencoded device such as punch-cards or raised structures in a groovehaving instructions recorded thereon, a media such as those supportingthe internet or an intranet, or a magnetic storage device. Note that thecomputer-usable or computer-readable medium could even be a suitablemedium upon which the program is stored, scanned, compiled, interpreted,or otherwise processed in a suitable manner, if necessary, and thenstored in a computer memory. In the context of the present disclosure, acomputer-usable or computer-readable, storage medium may be any tangiblemedium that can contain or store a program for use by or in connectionwith the instruction execution system, apparatus, or device.

In some implementations, a computer readable signal medium may include apropagated data signal with computer readable program code embodiedtherein, for example, in baseband or as part of a carrier wave. In someimplementations, such a propagated signal may take any of a variety offorms, including, but not limited to, electro-magnetic, optical, or anysuitable combination thereof. In some implementations, the computerreadable program code may be transmitted using any appropriate medium,including but not limited to the internet, wireline, optical fibercable, RF, etc. In some implementations, a computer readable signalmedium may be any computer readable medium that is not a computerreadable storage medium and that can communicate, propagate, ortransport a program for use by or in connection with an instructionexecution system, apparatus, or device.

In some implementations, computer program code for carrying outoperations of the present disclosure may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java®, Smalltalk, C++ or the like.Java® and all Java-based trademarks and logos are trademarks orregistered trademarks of Oracle and/or its affiliates. However, thecomputer program code for carrying out operations of the presentdisclosure may also be written in conventional procedural programminglanguages, such as the “C” programming language, PASCAL, or similarprogramming languages, as well as in scripting languages such asJavascript, PERL, or Python. The program code may execute entirely onthe user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough a local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theinternet using an Internet Service Provider). In some implementations,electronic circuitry including, for example, programmable logiccircuitry, field-programmable gate arrays (FPGAs) or other hardwareaccelerators, micro-controller units (MCUs), or programmable logicarrays (PLAs) may execute the computer readable programinstructions/code by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present disclosure.

In some implementations, the flowchart and block diagrams in the figuresillustrate the architecture, functionality, and operation of possibleimplementations of apparatus (systems), methods and computer programproducts according to various implementations of the present disclosure.Each block in the flowchart and/or block diagrams, and combinations ofblocks in the flowchart and/or block diagrams, may represent a module,segment, or portion of code, which comprises one or more executablecomputer program instructions for implementing the specified logicalfunction(s)/act(s). These computer program instructions may be providedto a processor of a general purpose computer, special purpose computer,or other programmable data processing apparatus to produce a machine,such that the computer program instructions, which may execute via theprocessor of the computer or other programmable data processingapparatus, create the ability to implement one or more of thefunctions/acts specified in the flowchart and/or block diagram block orblocks or combinations thereof. It should be noted that, in someimplementations, the functions noted in the block(s) may occur out ofthe order noted in the figures (or combined or omitted). For example,two blocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

In some implementations, these computer program instructions may also bestored in a computer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks or combinations thereof.

In some implementations, the computer program instructions may also beloaded onto a computer or other programmable data processing apparatusto cause a series of operational steps to be performed (not necessarilyin a particular order) on the computer or other programmable apparatusto produce a computer implemented process such that the instructionswhich execute on the computer or other programmable apparatus providesteps for implementing the functions/acts (not necessarily in aparticular order) specified in the flowchart and/or block diagram blockor blocks or combinations thereof.

Referring now to the example implementation of FIG. 1 , there is shownwrite process 10 that may reside on and may be executed by a computer(e.g., computer 12), which may be connected to a network (e.g., network14) (e.g., the internet or a local area network). Examples of computer12 (and/or one or more of the client electronic devices noted below) mayinclude, but are not limited to, a storage system (e.g., a NetworkAttached Storage (NAS) system, a Storage Area Network (SAN)), a personalcomputer(s), a laptop computer(s), mobile computing device(s), a servercomputer, a series of server computers, a mainframe computer(s), or acomputing cloud(s). As is known in the art, a SAN may include one ormore of the client electronic devices, including a Redundant Array ofInexpensive Disks/Redundant Array of Independent Disks (RAID) device anda NAS system. In some implementations, each of the aforementioned may begenerally described as a computing device. In certain implementations, acomputing device may be a physical or virtual device. In manyimplementations, a computing device may be any device capable ofperforming operations, such as a dedicated processor, a portion of aprocessor, a virtual processor, a portion of a virtual processor,portion of a virtual device, or a virtual device. In someimplementations, a processor may be a physical processor or a virtualprocessor. In some implementations, a virtual processor may correspondto one or more parts of one or more physical processors. In someimplementations, the instructions/logic may be distributed and executedacross one or more processors, virtual or physical, to execute theinstructions/logic. Computer 12 may execute an operating system, forexample, but not limited to, Microsoft® Windows®; Mac® OS X®; Red Hat®Linux®, Windows® Mobile, Chrome OS, Blackberry OS, Fire OS, or a customoperating system. (Microsoft and Windows are registered trademarks ofMicrosoft Corporation in the United States, other countries or both; Macand OS X are registered trademarks of Apple Inc. in the United States,other countries or both; Red Hat is a registered trademark of Red HatCorporation in the United States, other countries or both; and Linux isa registered trademark of Linus Torvalds in the United States, othercountries or both).

In some implementations, as will be discussed below in greater detail, awrite process, such as write process 10 of FIG. 1 , may submit, by acomputing device, a write for a write-request equal to a size of validdata in a segment. The write-request may be decomposed into RAIDelements and corresponding parity stripe elements. Parity for RAIDstripes may be calculated using only valid RAID elements of the RAIDelements. A write for all the valid RAID elements and the correspondingparity stripe elements may be issued. An unmap command may be issued toat least a portion of the segment that is invalid.

In some implementations, the instruction sets and subroutines of writeprocess 10, which may be stored on storage device, such as storagedevice 16, coupled to computer 12, may be executed by one or moreprocessors and one or more memory architectures included within computer12. In some implementations, storage device 16 may include but is notlimited to: a hard disk drive; all forms of flash memory storagedevices; a tape drive; an optical drive; a RAID array (or other array);a random access memory (RAM); a read-only memory (ROM); or combinationthereof. In some implementations, storage device 16 may be organized asan extent, an extent pool, a RAID extent (e.g., an example 4D+1P R5,where the RAID extent may include, e.g., five storage device extentsthat may be allocated from, e.g., five different storage devices), amapped RAID (e.g., a collection of RAID extents), or combinationthereof.

In some implementations, network 14 may be connected to one or moresecondary networks (e.g., network 18), examples of which may include butare not limited to: a local area network; a wide area network or othertelecommunications network facility; or an intranet, for example. Thephrase “telecommunications network facility,” as used herein, may referto a facility configured to transmit, and/or receive transmissionsto/from one or more mobile client electronic devices (e.g., cellphones,etc.) as well as many others.

In some implementations, computer 12 may include a data store, such as adatabase (e.g., relational database, object-oriented database,triplestore database, etc.) and may be located within any suitablememory location, such as storage device 16 coupled to computer 12. Insome implementations, data, metadata, information, etc. describedthroughout the present disclosure may be stored in the data store. Insome implementations, computer 12 may utilize any known databasemanagement system such as, but not limited to, DB2, in order to providemulti-user access to one or more databases, such as the above notedrelational database. In some implementations, the data store may also bea custom database, such as, for example, a flat file database or an XMLdatabase. In some implementations, any other form(s) of a data storagestructure and/or organization may also be used. In some implementations,write process 10 may be a component of the data store, a standaloneapplication that interfaces with the above noted data store and/or anapplet/application that is accessed via client applications 22, 24, 26,28. In some implementations, the above noted data store may be, in wholeor in part, distributed in a cloud computing topology. In this way,computer 12 and storage device 16 may refer to multiple devices, whichmay also be distributed throughout the network.

In some implementations, computer 12 may execute a storage managementapplication (e.g., storage management application 21), examples of whichmay include, but are not limited to, e.g., a storage system application,a cloud computing application, a data synchronization application, adata migration application, a garbage collection application, or otherapplication that allows for the implementation and/or management of datain a clustered (or non-clustered) environment (or the like). In someimplementations, write process 10 and/or storage management application21 may be accessed via one or more of client applications 22, 24, 26,28. In some implementations, write process 10 may be a standaloneapplication, or may be an applet/application/script/extension that mayinteract with and/or be executed within storage management application21, a component of storage management application 21, and/or one or moreof client applications 22, 24, 26, 28. In some implementations, storagemanagement application 21 may be a standalone application, or may be anapplet/application/script/extension that may interact with and/or beexecuted within write process 10, a component of write process 10,and/or one or more of client applications 22, 24, 26, 28. In someimplementations, one or more of client applications 22, 24, 26, 28 maybe a standalone application, or may be anapplet/application/script/extension that may interact with and/or beexecuted within and/or be a component of write process 10 and/or storagemanagement application 21. Examples of client applications 22, 24, 26,28 may include, but are not limited to, e.g., a storage systemapplication, a cloud computing application, a data synchronizationapplication, a data migration application, a garbage collectionapplication, or other application that allows for the implementationand/or management of data in a clustered (or non-clustered) environment(or the like), a standard and/or mobile web browser, an emailapplication (e.g., an email client application), a textual and/or agraphical user interface, a customized web browser, a plugin, anApplication Programming Interface (API), or a custom application. Theinstruction sets and subroutines of client applications 22, 24, 26, 28,which may be stored on storage devices 30, 32, 34, 36, coupled to clientelectronic devices 38, 40, 42, 44, may be executed by one or moreprocessors and one or more memory architectures incorporated into clientelectronic devices 38, 40, 42, 44.

In some implementations, one or more of storage devices 30, 32, 34, 36,may include but are not limited to: hard disk drives; flash drives, tapedrives; optical drives; RAID arrays; random access memories (RAM); andread-only memories (ROM). Examples of client electronic devices 38, 40,42, 44 (and/or computer 12) may include, but are not limited to, apersonal computer (e.g., client electronic device 38), a laptop computer(e.g., client electronic device 40), a smart/data-enabled, cellularphone (e.g., client electronic device 42), a notebook computer (e.g.,client electronic device 44), a tablet, a server, a television, a smarttelevision, a smart speaker, an Internet of Things (IoT) device, a media(e.g., video, photo, etc.) capturing device, and a dedicated networkdevice. Client electronic devices 38, 40, 42, 44 may each execute anoperating system, examples of which may include but are not limited to,Android™, Apple® iOS®, Mac® OS X®; Red Hat® Linux®, Windows® Mobile,Chrome OS, Blackberry OS, Fire OS, or a custom operating system.

In some implementations, one or more of client applications 22, 24, 26,28 may be configured to effectuate some or all of the functionality ofwrite process 10 (and vice versa). Accordingly, in some implementations,write process 10 may be a purely server-side application, a purelyclient-side application, or a hybrid server-side/client-side applicationthat is cooperatively executed by one or more of client applications 22,24, 26, 28 and/or write process 10.

In some implementations, one or more of client applications 22, 24, 26,28 may be configured to effectuate some or all of the functionality ofstorage management application 21 (and vice versa). Accordingly, in someimplementations, storage management application 21 may be a purelyserver-side application, a purely client-side application, or a hybridserver-side/client-side application that is cooperatively executed byone or more of client applications 22, 24, 26, 28 and/or storagemanagement application 21. As one or more of client applications 22, 24,26, 28, write process 10, and storage management application 21, takensingly or in any combination, may effectuate some or all of the samefunctionality, any description of effectuating such functionality viaone or more of client applications 22, 24, 26, 28, write process 10,storage management application 21, or combination thereof, and anydescribed interaction(s) between one or more of client applications 22,24, 26, 28, write process 10, storage management application 21, orcombination thereof to effectuate such functionality, should be taken asan example only and not to limit the scope of the disclosure.

In some implementations, one or more of users 46, 48, 50, 52 may accesscomputer 12 and write process 10 (e.g., using one or more of clientelectronic devices 38, 40, 42, 44) directly through network 14 orthrough secondary network 18. Further, computer 12 may be connected tonetwork 14 through secondary network 18, as illustrated with phantomlink line 54. Write process 10 may include one or more user interfaces,such as browsers and textual or graphical user interfaces, through whichusers 46, 48, 50, 52 may access write process 10.

In some implementations, the various client electronic devices may bedirectly or indirectly coupled to network 14 (or network 18). Forexample, client electronic device 38 is shown directly coupled tonetwork 14 via a hardwired network connection. Further, clientelectronic device 44 is shown directly coupled to network 18 via ahardwired network connection. Client electronic device 40 is shownwirelessly coupled to network 14 via wireless communication channel 56established between client electronic device 40 and wireless accesspoint (i.e., WAP) 58, which is shown directly coupled to network 14. WAP58 may be, for example, an IEEE 802.11a, 802.11b, 802.11g, 802.11n,802.11ac, Wi-Fi®, RFID, and/or Bluetooth™ (including Bluetooth™ LowEnergy) device that is capable of establishing wireless communicationchannel 56 between client electronic device 40 and WAP 58. Clientelectronic device 42 is shown wirelessly coupled to network 14 viawireless communication channel 60 established between client electronicdevice 42 and cellular network/bridge 62, which is shown by exampledirectly coupled to network 14.

In some implementations, some or all of the IEEE 802.11x specificationsmay use Ethernet protocol and carrier sense multiple access withcollision avoidance (i.e., CSMA/CA) for path sharing. The various802.11x specifications may use phase-shift keying (i.e., PSK) modulationor complementary code keying (i.e., CCK) modulation, for example.Bluetooth™ (including Bluetooth™ Low Energy) is a telecommunicationsindustry specification that allows, e.g., mobile phones, computers,smart phones, and other electronic devices to be interconnected using ashort-range wireless connection. Other forms of interconnection (e.g.,Near Field Communication (NFC)) may also be used.

In some implementations, various I/O requests (e.g., I/O request 15) maybe sent from, e.g., client applications 22, 24, 26, 28 to, e.g.,computer 12. Examples of I/O request 15 may include but are not limitedto, data write requests (e.g., a request that content be written tocomputer 12) and data read requests (e.g., a request that content beread from computer 12).

Data Storage System:

Referring also to the example implementation of FIGS. 2-3 (e.g., wherecomputer 12 may be configured as a data storage system), computer 12 mayinclude storage processor 100 and a plurality of storage targets (e.g.,storage targets 102, 104, 106, 108, 110). In some implementations,storage targets 102, 104, 106, 108, 110 may include any of theabove-noted storage devices. In some implementations, storage targets102, 104, 106, 108, 110 may be configured to provide various levels ofperformance and/or high availability. For example, storage targets 102,104, 106, 108, 110 may be configured to form a non-fully-duplicativefault-tolerant data storage system (such as a non-fully-duplicative RAIDdata storage system), examples of which may include but are not limitedto: RAID 3 arrays, RAID 4 arrays, RAID 5 arrays, and/or RAID 6 arrays.It will be appreciated that various other types of RAID arrays may beused without departing from the scope of the present disclosure.

While in this particular example, computer 12 is shown to include fivestorage targets (e.g., storage targets 102, 104, 106, 108, 110), this isfor example purposes only and is not intended limit the presentdisclosure. For instance, the actual number of storage targets may beincreased or decreased depending upon, e.g., the level ofredundancy/performance/capacity required.

Further, the storage targets (e.g., storage targets 102, 104, 106, 108,110) included with computer 12 may be configured to form a plurality ofdiscrete storage arrays. For instance, and assuming for example purposesonly that computer 12 includes, e.g., ten discrete storage targets, afirst five targets (of the ten storage targets) may be configured toform a first RAID array and a second five targets (of the ten storagetargets) may be configured to form a second RAID array.

In some implementations, one or more of storage targets 102, 104, 106,108, 110 may be configured to store coded data (e.g., via storagemanagement process 21), wherein such coded data may allow for theregeneration of data lost/corrupted on one or more of storage targets102, 104, 106, 108, 110. Examples of such coded data may include but isnot limited to parity data and Reed-Solomon data. Such coded data may bedistributed across all of storage targets 102, 104, 106, 108, 110 or maybe stored within a specific storage target.

Examples of storage targets 102, 104, 106, 108, 110 may include one ormore data arrays, wherein a combination of storage targets 102, 104,106, 108, 110 (and any processing/control systems associated withstorage management application 21) may form data array 112.

The manner in which computer 12 is implemented may vary depending upone.g., the level of redundancy/performance/capacity required. Forexample, computer 12 may be configured as a SAN (i.e., a Storage AreaNetwork), in which storage processor 100 may be, e.g., a dedicatedcomputing system and each of storage targets 102, 104, 106, 108, 110 maybe a RAID device. An example of storage processor 100 may include but isnot limited to a VPLEX™, VNX™, TRIDENT™, or Unity™ system offered byDell EMC™ of Hopkinton, Mass.

In the example where computer 12 is configured as a SAN, the variouscomponents of computer 12 (e.g., storage processor 100, and storagetargets 102, 104, 106, 108, 110) may be coupled using networkinfrastructure 114, examples of which may include but are not limited toan Ethernet (e.g., Layer 2 or Layer 3) network, a fiber channel network,an InfiniBand network, or any other circuit switched/packet switchednetwork.

As discussed above, various I/O requests (e.g., I/O request 15) may begenerated. For example, these I/O requests may be sent from, e.g.,client applications 22, 24, 26, 28 to, e.g., computer 12.Additionally/alternatively (e.g., when storage processor 100 isconfigured as an application server or otherwise), these I/O requestsmay be internally generated within storage processor 100 (e.g., viastorage management process 21). Examples of I/O request 15 may includebut are not limited to data write request 116 (e.g., a request thatcontent 118 be written to computer 12) and data read request 120 (e.g.,a request that content 118 be read from computer 12).

In some implementations, during operation of storage processor 100,content 118 to be written to computer 12 may be received and/orprocessed by storage processor 100 (e.g., via storage management process21). Additionally/alternatively (e.g., when storage processor 100 isconfigured as an application server or otherwise), content 118 to bewritten to computer 12 may be internally generated by storage processor100 (e.g., via storage management process 21).

As discussed above, the instruction sets and subroutines of storagemanagement application 21, which may be stored on storage device 16included within computer 12, may be executed by one or more processorsand one or more memory architectures included with computer 12.Accordingly, in addition to being executed on storage processor 100,some or all of the instruction sets and subroutines of storagemanagement application 21 (and/or write process 10) may be executed byone or more processors and one or more memory architectures includedwith data array 112.

In some implementations, storage processor 100 may include front endcache memory system 122. Examples of front end cache memory system 122may include but are not limited to a volatile, solid-state, cache memorysystem (e.g., a dynamic RAM cache memory system), a non-volatile,solid-state, cache memory system (e.g., a flash-based, cache memorysystem), and/or any of the above-noted storage devices.

In some implementations, storage processor 100 may initially storecontent 118 within front end cache memory system 122. Depending upon themanner in which front end cache memory system 122 is configured, storageprocessor 100 (e.g., via storage management process 21) may immediatelywrite content 118 to data array 112 (e.g., if front end cache memorysystem 122 is configured as a write-through cache) or may subsequentlywrite content 118 to data array 112 (e.g., if front end cache memorysystem 122 is configured as a write-back cache).

In some implementations, one or more of storage targets 102, 104, 106,108, 110 may include a backend cache memory system. Examples of thebackend cache memory system may include but are not limited to avolatile, solid-state, cache memory system (e.g., a dynamic RAM cachememory system), a non-volatile, solid-state, cache memory system (e.g.,a flash-based, cache memory system), and/or any of the above-notedstorage devices.

Storage Targets:

As discussed above, one or more of storage targets 102, 104, 106, 108,110 may be a RAID device. For instance, and referring also to FIG. 3 ,there is shown example target 150, wherein target 150 may be one exampleimplementation of a RAID implementation of, e.g., storage target 102,storage target 104, storage target 106, storage target 108, and/orstorage target 110. An example of target 150 may include but is notlimited to a VPLEX™, VNX™, TRIDENT™, or Unity™ system offered by DellEMC™ of Hopkinton, Mass. Examples of storage devices 154, 156, 158, 160,162 may include one or more electro-mechanical hard disk drives, one ormore solid-state/flash devices, and/or any of the above-noted storagedevices. It will be appreciated that while the term “disk” or “drive”may be used throughout, these may refer to and be used interchangeablywith any types of appropriate storage devices as the context andfunctionality of the storage device permits.

In some implementations, target 150 may include storage processor 152and a plurality of storage devices (e.g., storage devices 154, 156, 158,160, 162). Storage devices 154, 156, 158, 160, 162 may be configured toprovide various levels of performance and/or high availability (e.g.,via storage management process 21). For example, one or more of storagedevices 154, 156, 158, 160, 162 (or any of the above-noted storagedevices) may be configured as a RAID 0 array, in which data is stripedacross storage devices. By striping data across a plurality of storagedevices, improved performance may be realized. However, RAID 0 arraysmay not provide a level of high availability. Accordingly, one or moreof storage devices 154, 156, 158, 160, 162 (or any of the above-notedstorage devices) may be configured as a RAID 1 array, in which data ismirrored between storage devices. By mirroring data between storagedevices, a level of high availability may be achieved as multiple copiesof the data may be stored within storage devices 154, 156, 158, 160,162.

While storage devices 154, 156, 158, 160, 162 are discussed above asbeing configured in a RAID 0 or RAID 1 array, this is for examplepurposes only and not intended to limit the present disclosure, as otherconfigurations are possible. For example, storage devices 154, 156, 158,160, 162 may be configured as a RAID 3, RAID 4, RAID 5 or RAID 6 array.

While in this particular example, target 150 is shown to include fivestorage devices (e.g., storage devices 154, 156, 158, 160, 162), this isfor example purposes only and not intended to limit the presentdisclosure. For instance, the actual number of storage devices may beincreased or decreased depending upon, e.g., the level ofredundancy/performance/capacity required.

In some implementations, one or more of storage devices 154, 156, 158,160, 162 may be configured to store (e.g., via storage managementprocess 21) coded data, wherein such coded data may allow for theregeneration of data lost/corrupted on one or more of storage devices154, 156, 158, 160, 162. Examples of such coded data may include but arenot limited to parity data and Reed-Solomon data. Such coded data may bedistributed across all of storage devices 154, 156, 158, 160, 162 or maybe stored within a specific storage device.

The manner in which target 150 is implemented may vary depending upone.g., the level of redundancy/performance/capacity required. Forexample, target 150 may be a RAID device in which storage processor 152is a RAID controller card and storage devices 154, 156, 158, 160, 162are individual “hot-swappable” hard disk drives. Another example oftarget 150 may be a RAID system, examples of which may include but arenot limited to an NAS (i.e., Network Attached Storage) device or a SAN(i.e., Storage Area Network).

In some implementations, storage target 150 may execute all or a portionof storage management application 21. The instruction sets andsubroutines of storage management application 21, which may be stored ona storage device (e.g., storage device 164) coupled to storage processor152, may be executed by one or more processors and one or more memoryarchitectures included with storage processor 152. Storage device 164may include but is not limited to any of the above-noted storagedevices.

As discussed above, computer 12 may be configured as a SAN, whereinstorage processor 100 may be a dedicated computing system and each ofstorage targets 102, 104, 106, 108, 110 may be a RAID device.Accordingly, when storage processor 100 processes data requests 116,120, storage processor 100 (e.g., via storage management process 21) mayprovide the appropriate requests/content (e.g., write request 166,content 168 and read request 170) to, e.g., storage target 150 (which isrepresentative of storage targets 102, 104, 106, 108 and/or 110).

In some implementations, during operation of storage processor 152,content 168 to be written to target 150 may be processed by storageprocessor 152 (e.g., via storage management process 21). Storageprocessor 152 may include cache memory system 172. Examples of cachememory system 172 may include but are not limited to a volatile,solid-state, cache memory system (e.g., a dynamic RAM cache memorysystem) and/or a non-volatile, solid-state, cache memory system (e.g., aflash-based, cache memory system). During operation of storage processor152, content 168 to be written to target 150 may be received by storageprocessor 152 (e.g., via storage management process 21) and initiallystored (e.g., via storage management process 21) within front end cachememory system 172.

In some log-structured storage systems, ingesting data (either newwrites or over-writes) is generally always written to an empty segment.This segment is generally parity-protected (e.g., RAID-5, RAID-6) andlarge in size (e.g., 2 MB) to minimize the number of segments that needto be tracked in the storage system. There may be several use cases whenflushing dirty data into these segments, or when ingesting new writesdirectly into these segments, that there is not enough data tocompletely fill the segment. In such a scenario, rest of the segment ispadded with zeros and parity is calculated on the full segment.

Padding zeros to fill the segment has may have at least two example andnon-limiting disadvantages. For example, writing zeros to the SSD maycause write-amplification (i.e., SSD-wear). As another example,including padded-zeros in parity calculation costs CPU-cycles, but hasno effect on the generated parity. This may be true for, e.g., RAID-5and first parity of RAID-6. For second parity of RAID-6, it may dependon the algorithm chosen. As such, to address at least the above-notedproblems, the present disclosure may use a substitute technique in placeof padding with zeroes, discussed in greater detail below.

The Write Process:

As discussed above and referring also at least to the exampleimplementations of FIGS. 4-5 , write process 10 may submit 400, by acomputing device, a write for a write-request equal to a size of validdata in a segment. Write process 10 may decompose 402 the write-requestinto RAID elements and corresponding parity stripe elements. Writeprocess 10 may calculate 404 parity for RAID stripes using only validRAID elements of the RAID elements. Write process 10 may issue 406 awrite for all the valid RAID elements and the corresponding paritystripe elements. Write process 10 may issue 408 an unmap command to atleast a portion of the segment that is invalid.

Referring at least to the example implementation of FIG. 5 , a 4D+1P 2MB segment 500 with a 64k element size is shown. It will be appreciatedthat while the discussion may include examples of a segment that may beparity protected using either RAID-5 and RAID-6, any appropriate parityprotection may be used without departing from the scope of the presentdisclosure. As such, the use of RAID-5 or RAID-6 implementations shouldbe taken as example only and not to otherwise limit the scope of thepresent disclosure.

In some implementations, write process 10 may submit 400, by a computingdevice, a write for a write-request equal to a size of valid data in asegment. For instance, a typical storage system using log-structuredwrites may pad with zeros and always issue a write equal to the size ofthe segment; however, in some implementations, write process 10 (e.g.,via Mapper) may instead only submit 400 writes equal to the size ofvalid data in the segment. For example, and referring to segment 500 ofFIG. 5 , for an example and non-limiting size of a 2 MB segment, thesize of the write request issued by Mapper may be anywhere up to 2 MB.

In some implementations, write process 10 may decompose 402 thewrite-request into RAID elements and corresponding parity stripeelements. For instance, write process 10 may decompose 402 thewrite-request into RAID elements and corresponding parity stripeelements. As an example, and referring to segment 500 of FIG. 5 , writeprocess 10 (e.g., via Mapper) may issue a write-request of size 64k.Write process 10 may then decompose 402 the request into 10 RAIDelements, which completely fills two parity-stripes and partially fillsa third parity stripe. In some implementations, the RAID elements mayinclude sub-RAID elements. That is, it will be appreciated that thepresent disclosure may be extended to sub-RAID elements as well to avoidpadding within RAID elements. As such, the use of RAID elements that arenot sub-RAID elements should be taken as example only and not tootherwise limit the scope of the present disclosure.

In some implementations, write process 10 may calculate 404 parity forRAID stripes using only valid RAID elements of the RAID elements. Forexample, write process 10 may calculate 404 parity for RAID stripes withonly valid RAID elements. For instance, and referring to segment 500 ofFIG. 5 , write process 10 may calculate 404 parity using all RAIDelements for the first two parity stripes (noted as Y in the firststripe and R in the second stripe). For the third parity stripe, writeprocess 10 may calculate parity using only 2 valid RAID elements (notedas G in the third stripe). For the fourth parity stripe (noted as X),write process 10 will not calculate parity at all, as there are no validRAID elements.

In some implementations, write process 10 may issue 406 a write for allthe valid RAID elements and the corresponding parity stripe elements.For example, write process 10 may issue 406 writes to, e.g., asolid-state drive (SSD) or similar storage device, for all valid RAIDelements and their corresponding parity elements. For instance, andreferring to segment 500 of FIG. 5 , there is shown 10 valid RAIDelements (noted as Y in the first stripe, R in the second stripe, and Gin the third stripe) and 3 valid parity elements (noted as Y-parity inthe first stripe, R-parity in the second stripe, and G-parity in thethird stripe).

In some implementations, write process 10 may issue 408 an unmap commandto at least a portion of the segment that is invalid, where the portionof the segment may include RAID elements that are invalid in the segmentand/or the corresponding parity stripe elements that are invalid in thesegment. For example, write process 10 may issue 408 an unmap command tothe RAID elements and parity elements that are invalid in the segment.For instance, and referring to segment 500 of FIG. 5 , there is shown 6invalid RAID elements (noted as X in the third stripe and fourth stripe)and 1 invalid parity element (also noted as X under the G-parity of thethird stripe). It is these RAID and parity elements that will be issuedthe unmap command, as they are invalid.

In some implementations, issuing the unmap command to the RAID elementsand corresponding parity stripe elements that are invalid in the segmentmay result in returning zeros on subsequent reads of the RAID elementsand corresponding parity stripe elements that are invalid in thesegment, such that the zeros may be returned on the subsequent reads ofthe RAID elements and corresponding parity stripe elements that areinvalid in the segment without writing the zeros. That is, issuing theunmap command to invalid RAID elements may result in returning zeros onsubsequent read of the invalid RAID elements (which is needed for theRAID consistency of the segment) without actually writing zeros. As aresult, SSD-wear may be reduced.

The terminology used herein is for the purpose of describing particularimplementations only and is not intended to be limiting of thedisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. As used herein, the language “at least one of A, B,and C” (and the like) should be interpreted as covering only A, only B,only C, or any combination of the three, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps (notnecessarily in a particular order), operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps (not necessarily in a particular order),operations, elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents (e.g., ofall means or step plus function elements) that may be in the claimsbelow are intended to include any structure, material, or act forperforming the function in combination with other claimed elements asspecifically claimed. The description of the present disclosure has beenpresented for purposes of illustration and description, but is notintended to be exhaustive or limited to the disclosure in the formdisclosed. Many modifications, variations, substitutions, and anycombinations thereof will be apparent to those of ordinary skill in theart without departing from the scope and spirit of the disclosure. Theimplementation(s) were chosen and described in order to explain theprinciples of the disclosure and the practical application, and toenable others of ordinary skill in the art to understand the disclosurefor various implementation(s) with various modifications and/or anycombinations of implementation(s) as are suited to the particular usecontemplated.

Having thus described the disclosure of the present application indetail and by reference to implementation(s) thereof, it will beapparent that modifications, variations, and any combinations ofimplementation(s) (including any modifications, variations,substitutions, and combinations thereof) are possible without departingfrom the scope of the disclosure defined in the appended claims.

What is claimed is:
 1. A computer-implemented method comprising:submitting, by a computing device, a write for a write-request equal toa size of valid data in a segment; decomposing the write-request intoRAID elements and corresponding parity stripe elements; calculatingparity for RAID stripes using only valid RAID elements of the RAIDelements; issuing a write for all the valid RAID elements and thecorresponding parity stripe elements; and based at least in part on thecalculation of the parity for the RAID stripes using only the valid RAIDelements of the RAID elements, issuing an unmap command to at least aportion of the segment that is invalid resulting in returning zeros onsubsequent reads of the RAID elements and corresponding parity stripeelements that are invalid in the segment without writing the zeros. 2.The computer-implemented method of claim 1 wherein the RAID elementsinclude sub-RAID elements.
 3. The computer-implemented method of claim 1wherein at least the portion of the segment includes RAID elements thatare invalid in the segment.
 4. The computer-implemented method of claim3 wherein at least the portion of the segment further includescorresponding parity stripe elements that are invalid in the segment. 5.The computer-implemented method of claim 1 wherein the segment is parityprotected using one of RAID-5 and RAID-6.
 6. A computer program productresiding on a non-transitory computer readable storage medium having aplurality of instructions stored thereon which, when executed across oneor more processors, causes at least a portion of the one or moreprocessors to perform operations comprising: submitting a write for awrite-request equal to a size of valid data in a segment; decomposingthe write-request into RAID elements and corresponding parity stripeelements; calculating parity for RAID stripes using only valid RAIDelements of the RAID elements; issuing a write for all the valid RAIDelements and the corresponding parity stripe elements; and based atleast in part on the calculation of the parity for the RAID stripesusing only the valid RAID elements of the RAID elements, issuing anunmap command to at least a portion of the segment that is invalidresulting in returning zeros on subsequent reads of the RAID elementsand corresponding parity stripe elements that are invalid in the segmentwithout writing the zeros.
 7. The computer program product of claim 6wherein the RAID elements include sub-RAID elements.
 8. The computerprogram product of claim 6 wherein at least the portion of the segmentincludes RAID elements that are invalid in the segment.
 9. The computerprogram product of claim 8 wherein at least the portion of the segmentfurther includes corresponding parity stripe elements that are invalidin the segment.
 10. The computer program product of claim 6 wherein thesegment is parity protected using one of RAID-5 and RAID-6.
 11. Acomputing system including one or more processors and one or morememories configured to perform operations comprising: submitting a writefor a write-request equal to a size of valid data in a segment;decomposing the write-request into RAID elements and correspondingparity stripe elements; calculating parity for RAID stripes using onlyvalid RAID elements of the RAID elements; issuing a write for all thevalid RAID elements and the corresponding parity stripe elements; andbased at least in part on the calculation of the parity for the RAIDstripes using only the valid RAID elements of the RAID elements, issuingan unmap command to at least a portion of the segment that is invalidresulting in returning zeros on subsequent reads of the RAID elementsand corresponding parity stripe elements that are invalid in the segmentwithout writing the zeros.
 12. The computing system of claim 11 whereinthe RAID elements include sub-RAID elements.
 13. The computing system ofclaim 11 wherein at least the portion of the segment includes RAIDelements that are invalid in the segment and corresponding parity stripeelements that are invalid in the segment.
 14. The computing system ofclaim 11 wherein the segment is parity protected using one of RAID-5 andRAID-6.